The combination of low cost and high quality output have recently made ink-jet printers a popular alternative to other types of non-impact printers such as laser printers.
The ink-jet printing process involves the ejection of fine droplets of ink onto a print medium such as paper in response to electrical signals generated by a microprocessor. Typically, an ink-jet printer utilizes a pen set mounted on a carriage that is moved relative to the surface of a print medium. In commercially available ink-jet color printers, such as the DESKJET™ printer available from Hewlett-Packard Company, a four-pen set including cyan, yellow, magenta and black inks is generally employed to achieve the necessary color combinations.
A typical pen includes print heads with orifice plates that have very small nozzles (typically 10-50 μm diameter) through which the ink droplets are ejected. Adjacent these nozzles are ink chambers where ink is stored prior to ejection. U.S. Pat. No. 5,181,045 (incorporated by reference herein) discloses a typical channel between the ink chamber and the nozzle.
Ink drop ejection is currently achieved either thermally or piezoelectrically. In thermal ink-jet printing, each nozzle is associated with a resistor element. Each resistor element is in turn connected to a microprocessor, signals from which direct one or more resistor elements to heat up rapidly. The heating of the resistor elements causes a rapid expansion of ink vapor that forces a drop of ink through the associated nozzle onto the print medium. In piezoelectric ink-jet printing, ink droplets are ejected due to the vibrations of piezoelectric crystals stimulated by electrical signals generated by the microprocessor.
Interactions between the ink and pen architecture (e.g., the resistor element, nozzle, etc.) strongly influence the reliability of pen performance. In addition, interactions between the ink and both the surface and bulk of the print medium play a key role in determining print quality. A significant amount of research has recently been conducted to produce improved ink compositions for ink-jet printers that exhibit favorable interactions with both the pen architecture and the print medium.
There are many demanding performance requirements for colorants and inks used in ink-jet printing. For example, they desirably provide sharp, non-feathered images having good water-fastness, light-fastness and optical density. Optical density is the degree of darkness and/or spectral reflectance of printed colors.
There is a need for inks which are suitable for both thermal and piezo ink-jet printers, have high color strength, and produce images having a high light-fastness and water-fastness when printed on a substrate. There have been many attempts by industry to produce fast drying inks with good bleed control. When surfactants are used for the purpose of dry-time improvement, one often sees a concomitant bleed control improvement, however, often at the expense of print quality—more specifically, edge acuity. Additionally, the use of surfactants in the ink compositions can lead to optical density losses. Thus, a need still remains for ink compositions for use in ink-jet printing which have faster dry time as well as maintaining other desirable properties of such inks, such as waterfastness, bleed control, and halo control.